Olympic Opta question

[NWW.]

Hello all - this is my first post, looking for some info.

I just picked up this 1958 Olympic Opta "Bella", model 5700W . This the first German radio in my collection, all my other tube radios are American made.

I have a question regarding the sound. It seems to be working well, with good sound and sensitivity on all three bands. However, when the audio is switched to anything other than "voice" (i.e. jazz, bass, orch) the sound becomes "buzzy" almost sounding like the station is not quite tuned in - even though it is tuned perfectly. This becomes more apparent after the set has had a few minutes to warm up all the way.

Looking for an easy fix, I thought I would clean the sliding contact pins that move into position when the tone switches are depressed, but that doesn't seem to have corrected the problem. I'm not very familiar with these German sets...anyone have any suggestions?

Since this photo was taken, I've also been able to clean the speaker cloth quite a bit more.

 

[gadget73]

Could be the speaker is damaged. Try hooking up a different speaker and see if anything changes. If you're lucky, its just dust bunnies and dead bugs laying on the speaker cone, if not the speaker may be torn or have other problems.

I'd also vote for a complete re-cap. German sets are tight underneath but the mono sets aren't horrible to deal with. I have a couple of similar size and they're manageable.

 

[cubby01]

From your description I wouldn't think it would be speaker problems, but if it's an easy switch, or you have an external speaker jack try it.

My initial guess is one you've tried...that it's been setting on 'voice' for many years, and maybe just have bad contacts on the other switch settings.

Jazz, bass, and orch most likely have some EQ circuitry so some bad caps or out of spec resistors in those circuits would be my next check. Time to locate a schematic.

 

[RWood]

Very nice looking radio, welcome to the forum.

This becomes more apparent after the set has had a few minutes to warm up all the way.

In addition to the good advice already given, I think this sounds like a leaking coupling capacitor going to the grid your power tube. A very frequently encountered situation.

That set uses a single EL84 power tube, and the grid (signal input) is pin 2. You can measure for DC voltage on that pin to see if in fact the capacitor is leaking (there should be close to 0 VDC there, anything more indicates leakage). Or you can skip the measurement and replace that cap - it will only help.

If you follow what's connected to pin 2, tracing it back to the plate of the previous tube (pin 9 of the EABC80) you should see a capacitor, probably .022uF. Replace that capacitor with a Mallory 150 series or Orange Drop - something rated for at least 200V but 400V or 630V will work too.

This could be just the first of many caps that you replace, but based on your description, it is where I would start. And I strongly agree with cleaning the contacts on that timbre control.

RWood

 

[NWW.]

Thanks for all of the advice! I thought that some bad caps might be the issue - but always hopeful for an easy fix.

I actually haven't done any repair work myself - though I do understand the process. I have been really hesitant to do much on my own, because I would like to have someone walk me through it first, and don't have all of the necessary equipment either. I don't know if I will attempt any repair work by myself on this set, or try to have someone with better knowledge of foreign sets do it for me.